diff --git a/build/pkgs/tomli/spkg-install.in b/build/pkgs/tomli/spkg-install.in
index 7456ea0274d..e0d72afde3b 100644
--- a/build/pkgs/tomli/spkg-install.in
+++ b/build/pkgs/tomli/spkg-install.in
@@ -1,4 +1,7 @@
 cd src
 # tomli's build system, flit_core, has a runtime dependency on tomli.
+# Hence we make the uninstalled tomli sources available during the installation
+# and disable build isolation -- which would require a tomli wheel to
+# be available for setting up the build environment.
 export PYTHONPATH="$(pwd)"
 sdh_pip_install --no-build-isolation .